Dear Mr. Dad: My son has changed completely over the last few months, from a sweet kid to surly and rude. He deliberately upsets our younger children, mouths off to his mother and me, and spends all his time in his room or out with his friends—most of whom are new. He’s dropped out of all the things he used to love, like soccer and orchestra, and doesn’t seem the least bit concerned with personal hygiene. The other day my mom came to visit and asked me whether some animal had died in the house. I had to admit to that the smell was coming from my son. Is he on drugs and what should I do about it?

A: On one hand, a lot of what you’re describing is completely normal for teens—especially the smell issue and the rudeness. (Of course, just because something is normal doesn’t make it any easier to deal with.) On the other hand, behaviours like hanging out with a new group of friends and losing interest in activities he used to love are definitely red flags.

Let’s start with the easier stuff. Your first order of business is to sit down with your wife and come up with some ground rules for your son’s behavior—rules you both agree on and will stick to. Then, approach your son as a team. Remind him that although he may consider himself an adult, as long as he’s living in your home, you won’t tolerate bullying and he’ll need to treat people with respect. Don’t shout, don’t lose your temper, and keep the discussion short and to the point. Health and safety should be non-negotiable.

Next, talk about hygiene. Unfortunately, a lot of teens (girls as well as boys) go through a stage where they not only start smelling bad, but they also seemingly lose their sense of smell. And they’re genuinely surprised when someone points out that whenever they enter a room the paint peels, flowers wilt, and people pass out. Fortunately, most kids outgrow this stage within a few years. In the meantime, make sure your son’s bathroom is well stocked with soap, shampoo, toothpaste, and floss. Stay away from scented products and deodorants because they can be used to mask the underlying stench. If your son doesn’t get the hint, try requiring him to pass a sniff test before he’s allowed to leave the house. If all else fails, you may want to use the magic words: “You’ll never be able to get a girl to go out with you if you don’t start showering and brushing your teeth more often.”

Now, back to the drugs. There may be a perfectly reasonable explanation for his behavior (such as that he’s a teenager), so tell him—openly and calmly—that you’re worried and ask him what’s going on. If you sense that he’s covering something up or you’ve noticed a lot of symptoms (which include a red or flushed face, slurred speech, using breath mints, sudden drop in grades, wild mood swings, excessive sleep, dramatic weight loss or gain, money and other valuables disappearing, and pupils that are huge and don’t react to changes in lighting), you’ll have to take a more aggressive approach—but don’t try to do it on your own.

Start by educating yourself by vising drugfree.org—they have a lot of great information on prevention, intervention, treatment, and recovery. Then, talk to your son’s teachers, school administrators, and his pediatrician and ask them to help you help your son. The sooner you start, the better.